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United States Patent |
5,108,454
|
Rothschild
,   et al.
|
April 28, 1992
|
Below-the-knee prosthesis and method of making the same
Abstract
A prosthesis for fitting a below-the-knee amputee is disclosed and includes
a socket for receiving the stump of the below-the-knee amputee, a keel
having a peripheral groove formed about the periphery of a bottom portion
of the keel, a tubular shin member extending from the socket and
surrounding lateral and medial portions of the keel and filling the
peripheral grooves formed about the bottom portion of the keel leaving a
substantial portion of the bottom of the keel exposed. A resilient foot
member is then secured to the exposed portion of the keel with the
material of the tubular shin member being formed into the grooves of the
keel and maintaining such keel within the shin member. Also the method of
manufacturing such prosthesis.
Inventors:
|
Rothschild; Vernon R. (Cape St. Claire, MD);
Fox; John R. (Trappe, MD)
|
Assignee:
|
Rothschild's Orthopedic Appliances, Inc. (Forestville, MD)
|
Appl. No.:
|
493454 |
Filed:
|
March 14, 1990 |
Current U.S. Class: |
623/33; 623/53 |
Intern'l Class: |
A61F 002/60 |
Field of Search: |
623/33,32,29,53-56
264/DIG. 30
|
References Cited
U.S. Patent Documents
706498 | Aug., 1902 | Seeley.
| |
795734 | Jul., 1905 | Seeley.
| |
1436875 | Nov., 1922 | Greening.
| |
1884588 | Oct., 1932 | Davies | 623/53.
|
3909855 | Oct., 1975 | Barredo | 3/16.
|
4307056 | Dec., 1981 | Meyer | 623/33.
|
4473421 | Sep., 1984 | Gustafsson | 156/214.
|
4735754 | Apr., 1988 | Buckner | 264/40.
|
Primary Examiner: Shay; Randy C.
Assistant Examiner: Gualtieri; G.
Attorney, Agent or Firm: Sixbey, Friedman, Leedom & Ferguson
Claims
What is claimed:
1. A prosthesis for fitting a below-the-knee stump comprising:
a socket means for receiving the stump of a below-the-knee amputee,
a keel having a retaining means for retaining said keel in a predetermined
position with respect to said socket means, said retaining means including
a peripheral groove formed about the periphery of a bottom surface of said
keel,
a tubular shin member extending from said socket means and surrounding
lateral and medial portions of said keel and extending into said retaining
means leaving a substantial portion of said bottom surface of said keel
exposed, and
a resilient foot member secured to said exposed bottom surface of said
keel,
wherein said tubular shin member cooperates with said keel to maintain said
keel in said predetermined position.
2. The prosthesis as defined in claim 1, further comprising a transverse
groove formed in said bottom surface of said keel extending from a lateral
periphery of said keel to a medial periphery of said keel.
3. The prosthesis as defined in claim 2, wherein said tubular shin member
extends into said peripheral groove and said transverse groove in order to
maintain said keel in said predetermined position.
4. The prosthesis as defined in claim 3, wherein said tubular shin member
is molded from a copolymer sheet, and said sheet is molded into said
peripheral groove and said transverse groove.
5. The prosthesis as defined in claim 4, wherein said copolymer sheet is
polytetrabutylene.
6. The prosthesis as defined in claim 4, wherein said retaining means
further includes at least one bore in each of the medial and lateral sides
of said keel, and said copolymer material of said tubular shin member
projects into each of said bores.
7. The prosthesis as defined in claim 1, wherein said keel is formed of a
foam material.
8. The prosthesis as defined in claim 1, wherein said peripheral groove is
approximately 1/4 inch in width and approximately 1/8 inch in depth.
9. The prosthesis as defined in claim 2, wherein said transverse groove is
positioned approximately 1 inch posterior of a leading edge of said keel.
10. The prosthesis as defined in claim 2, wherein said transverse groove is
approximately 1/2 inch in width and approximately 1/8 inch in depth.
Description
TECHNICAL FIELD
This invention relates to a below-the-knee prosthesis and method of making
the same. More particularly, this invention relates to a light-weight
below-the-knee prosthesis having a foam keel portion such that a rubber
foot may be readily adhered thereto.
BACKGROUND OF THE INVENTION
An artificial leg or prosthesis for a person who has a below-the-knee
amputation and has tissues which are sensitive to the pressures and
friction associated with the use of a prosthesis presents a significant
problem if reasonably full use of the knee is to preserved. As is the case
with conventional prosthesis, these artificial limbs are usually fitted to
the stump of the leg below the knee and strapped to the leg above the knee
so that use of the knee for walking may be preserved. However, because
this limb is fitted to the stump and the stump and limb are not one in the
same, significant stresses during movement of the limb will tend to
irritate the stump in the area where it contacts the prosthesis.
Therefore, the need for a lightweight prosthesis is apparent particularly
when fitting very weak geriatric patients with this type of prosthesis.
Numerous attempts have been made to develop a prosthesis which is both
lightweight and structurally sound in order to perform functions similar
to that of the natural limb. Some of these attempts have included an
articulated toe and ankle section in an attempt to imitate nature by
duplicating the functions of the natural foot. The importance of the
cosmetic aspects of such an articulated limb are not to be denied,
however, the simulation of these joints as well as that of the weight of a
natural leg results in a limb which is difficult to maneuver due to an
extreme excess of weight. The prosthesis is not a natural limb and, as
mentioned above, cannot function in all respects as a natural integral
limb.
In one attempt to overcome the shortcomings associated with the use of a
below-the-knee prosthesis is set forth in U.S. Pat. No. 3,909,855 issued
to Barredo. This below-the-knee prosthesis is a hollow rigid lightweight
non-articulated prosthesis having a foreshortened foot which is fitted to
the stump of a below-the-knee amputee. This prosthesis is of a unitary
hollow shell formed of fiber glass and includes a foreshortened foot. This
foreshortened foot portion is shortened by a length approximately equal to
the toes of a natural foot and allows the prosthesis wearer to walk in a
manner somewhat like that of a natural walk. However, the foreshortened
foot exhibits no shock absorption characteristics and therefore any shock
to the foot portion of this prosthesis will be absorbed completely by the
stump of the wearer. Moreover, the foreshortened foot portion is not
cosmetically pleasing to either the wearer or others.
A currently favored simplification of the articulated toe and ankle
prosthesis is that of a prosthesis having a solid ankle portion and
cushioned toe, heel and sole attached thereto, commonly known as the SACH
foot design which is fixed to the bottom portion of the prosthesis.
In previously known SACH-type prosthesis, the socket portion of the
prosthesis was formed in a conventional manner. The socket may then be
adhered to a copolymer prosthesis having a solid ankle portion. Initially,
the copolymer completely encompassed the solid ankle and consequently the
cushioned or resilient heel was adhered directly to the bottom of the
prosthesis, however, a reliable bond between the resilient heel and the
copolymer prosthesis was not achievable due to the nature of the
copolymer.
In order to overcome the above-mentioned problem, the bottom of the solid
ankle portion was left exposed; i.e., with no copolymer material extending
thereover and consequently a strong adhesion could be formed between the
foam material of the solid ankle portion and the resilient material of the
heel portion. However, because a majority of the foam is removed from
within the prosthesis in order to significantly reduce the weight of the
prosthesis, during use the keel would detach from the copolymer material
of the prosthesis and pull out of the prosthesis resulting in a separation
between the resilient heel and the shin portion of the prosthesis thus
resulting in a lack of confidence in the structural integrity of the
prosthesis. Additionally, because the prosthesis was susceptible to such
structural damage, use of the prosthesis was limited to inactive
below-the-knee amputees.
Clearly, there is a pressing need for a lightweight and structurally sound
prosthesis that may be worn by both nonactive as well as active amputees
who can wear the prosthesis while performing any activity without fear of
any catastrophic failures.
SUMMARY OF THE INVENTION
A primary object of the present invention is to overcome the
above-mentioned shortcomings associated with the previously known
prostheses.
A particular object of the present invention is to provide a light weight
prosthesis which may be worn by either an active or inactive
below-the-knee amputee. This is achieved by removing substantially all of
the foam material used to construct the support structure for molding a
shin portion of the prosthesis thereon. This is carried out by grinding
away from an interior of the shin member foam material wherein the foam
material is accessed from both the proximal and distal ends of the
prosthesis.
Another object of the present invention is to provide a prosthesis wherein
the fear of catastrophic failure of the prosthesis is virtually
eliminated. This is carried out by forming a retaining means in the keel
portion of the prosthesis such that material forming the shin member will
essentially lock the keel within the shin so as to prevent the keel from
pulling out of the shin member during use.
A further object of the present invention is to reliably secure a resilient
foot to the bottom surface of the keel. This is carried out by temporarily
securing the foot to the bottom surface of the keel and forming channels
about the periphery of the surface. These channels are then completely
filled with an epoxy resin which reliably maintains the resilient foot in
place.
These as well as other objects of the present invention are achieved by
providing a prosthesis for fitting a below-the-knee stump including a
socket for receiving the stump of a below-the-knee amputee, a keel having
a peripheral groove formed about the periphery of a bottom surface thereof
as well as a transverse groove extending from a lateral periphery of the
keel to a medial periphery of the keel formed in the bottom surface. A
tubular shin member extending from the socket means and surrounding the
keel with a portion thereof extending into the retaining means while
leaving a substantial portion of the bottom surface of the keel exposed
and a resilient foot member secured to this exposed bottom surface.
The above-mentioned prosthesis is formed in accordance with the present
invention by forming a socket conforming to the stump of the
below-the-knee amputee, constructing a shin support including an ankle
block and the keel in accordance with the size and stature of the amputee
on the socket, machining a peripheral groove about the periphery of the
bottom surface of the keel and a transverse groove extending from the
lateral periphery to the medial periphery of the keel and the bottom
surface thereof for retaining the keel in a predetermined position with
respect to a shin member, and molding a sheet of copolymer material,
preferably polytetrabutylene about the shin support, and into the
retaining means and over the bottom surface of the keel to form the shin
member. Next, all of the copolymer material is removed from the bottom
surface of the keel except for that portion which has been molded into the
grooves, a substantial portion of the material used to construct the shin
support is removed from within the shin member and a resilient foot is
secured to the exposed bottom surface of the keel. Also formed in both the
lateral and medial sides of the keel are a plurality of bores for
receiving a portion of the molded sheet of copolymer material to aid in
maintaining the keel in the predetermined position with respect to the
shin member.
The above, as well as other objects of the present invention, will become
apparent from the drawings and detailed description set forth hereinbelow.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side elevational view of a prosthesis in accordance with the
present invention with the stump portion of a below-the-knee amputee
inserted therein.
FIG. 2 is a partially cross-section front elevational view of the
prosthesis of FIG. 1.
FIG. 3 is an elevational view of a keel and ankle block portion in
accordance with the present invention.
FIG. 4 is a bottom view of the keel illustrated in FIG. 3.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to the drawings and particularly to FIG. 1, a prosthesis 2 is
illustrated having a socket 4 for receiving a stump 6 of a below-the-knee
amputee. The prosthesis 2 of the present invention is formed of a 1/8"
sheet of copolymer material, preferably polytetrabutylene which is heated
in an oven and formed about a mold. This process will be described in
greater detail hereinbelow. The prosthesis 2 includes the socket 4 for
receiving the stump 6 and a shin portion 8 which extends downwardly from
the socket and about an ankle block 10 and keel 12 which are best seen in
FIG. 3. Attached to the bottom of the keel 12 is a resilient heal, such as
an OTTO BOCKTM.TM.]No. 1S19 resilient heel, sole and toe section more
commonly referred to as a foot 14. The foot 14 is adhesively secured to an
exposed bottom portion of the keel 12 which will be described in greater
detail hereinbelow.
As can be seen from FIG. 2, the upper portion of the shin 8 is fixed to the
socket 4 in a conventional manner and extends downwardly therefrom and
about the ankle block 10 and keel 12. The ankle block 10 and keel 12 are
best illustrated in FIG. 3 wherein these members are illustrated as
abutting one another at 17. During the manufacturing process of the
prosthesis, a suitable ankle block 10 and keel 12 are selected in
accordance with the size of the amputee to be fitted. The ankle block 10
is formed of a foam material such as OTTO BOCK.TM. Pedelin Foam No. 617H12
and Hardener No. 617P21 as is the keel 12. As can be noted, the keel 12
takes the shape of the upper region of the foot and it is the lateral or
outer side of the foot that is illustrated in FIG. 3. Once the appropriate
sized ankle block 10 and keel 12 have been selected, these members are
fixed relative to one another and the ankle block 10 is trimmed to achieve
a smooth transition between the ankle block 10 and keel 12. These members
are secured to one another in a conventional manner by way of an ankle
bolt (not shown) inserted through the bolt hole 13 which is later removed
when finishing the prosthesis.
As can be noted from FIG. 3, and as is better illustrated in FIG. 4, a
groove 18 is formed about the peripheral of the keel member with this
groove being approximately 1/4" wide and 1/8" deep. The groove 18 is in
the form of a cut-out and extends about the entire periphery of the bottom
of the keel 12. Also formed in the keel 12 is a transverse groove 20 which
extends from the lateral side 22 to the medial side 24 of the keel. This
groove is positioned approximately one inch posterior to the leading edge
of the keel and is approximately 1/2" wide and 1/8" deep. These grooves
may be easily formed in the foam material of the keel by way of a
hand-held grinder; however, in order to minimize manufacturing costs and
time, these grooves may be either molded or machined into the keel during
its original manufacture. Also formed in both the lateral side 22 and the
medial side 24 of the keel 12 are bores 26a through 26d. These bores are
approximately 5/16" wide and 1/4" deep. While the preferred embodiment
illustrates a pair of bores on each of the lateral and medial sides of the
keel 12, any number of such bores may be provided so long as the
structural integrity of the keel 12 is maintained. With the particular
pattern of grooves set forth in the bottom portion of the keel 12, raised
portions 28 and 30 are formed which contact the foot 14 when such foot is
positioned adjacent thereto. While in the preferred embodiment, only one
transverse groove 20 is illustrated, any number of grooves may again be
present so long as the structural integrity of the keel 12 is maintained
and a sufficient surface area is provided for contacting the foot 14. The
significance of the above-mentioned grooves 18 and 20 as well as the bores
26a-26d and the raised surfaces 28 and 30 will become apparent from a
discussion of the manufacturing process of the prosthesis set forth in
greater detail hereinbelow.
As mentioned previously, the two major concerns of the prostheses is the
effective weight and structural integrity of the prosthesis. By effective
weight, it is meant the actual distribution of the weight in proportion to
the overall weight. For example, the more weight which is distributed away
from the socket 4 of the prosthesis, the greater the force required to
maneuver such weight. Therefore, it is not only the overall weight of the
prosthesis which is of concern, but effective weight thereof. The
above-described prosthesis achieves both of these criteria and is
manufactured in the following manner.
Initially, a well-fitting positive mold of the residual limb of the
below-the-knee amputee is formed in a conventional manner. Check sockets
are often used to achieve this goal. The socket 4 is also manufactured in
a conventional manner from a PELITE.RTM. liner of 3/16" firm PELITE.RTM.
which is heated and molded over the cast in the conventional manner with a
nylon sheath being pulled over the PELITE.RTM. liner and sprayed with
silicone. Next, a 1/8" copolymer sheet, preferably of polytetrabutyline,
is heated in an oven and subsequently draped over the cast which is
positioned in a horizontal manner with the anterior of the mold facing
downward. This copolymer sheet is then seamed and vacuumed formed in a
conventional manner to fabricate the socket. Excess plastic is trimmed
about the cast with scissors with the remaining seam being flattened by
rolling a dowel across the seam while applying a suitable amount of
pressure. Care must be taken to assure that the area about the seam does
not become excessively thin. The socket is then allowed to cool for
approximately 30 minutes. After such time, a small hole is drilled in the
distal end of the socket and an air gun is used to remove the socket and
liner from the cast with a grinder being used to reduce the overall seam
to approximately 1/16". It should be noted that by not stretching the
copolymer material over the cast, once this material has set a minimal
amount of shrinkage will be experience.
The thus-formed positive mold is then cleaned and all excess plastic is
removed. The cast is then placed distal end up in a pipe jig and a 5-ply
sock is then pulled over the cast. The plastic socket is then put back on
the cast and a shin section is manufactured in the conventional manner
using a foam material such as OTTO BOCL# pedelin Foam No. 617H12 and a
Hardener No. 617P21. By positioning the socket on the cast, this will
prevent any distortions of the socket created by heat which is generated
by the curing foam. Once this foam mixture has cured, the socket may then
be removed from the cast.
An appropriate foot such as an OTTO BOCHT# No. 1S19 foot with pedelin keel
and ankle block is then selected in accordance with the size and stature
of the amputee to be fitted with the prosthesis. The now-formed shin and
socket section is then trimmed to an appropriate height and the ankle
block is fitted to the distal end thereof in a conventional manner. Once
this has been carried out, the thus-formed prosthesis is then positioned
on the patient and any height or alignment changes can be made in the shin
portion by cutting away portions of the foam and the subsequent
re-attachment thereof. It should be noted that the foam material may be
brittle and that care must be taken during this stage of the manufacturing
process in order not to damage the foam structure.
Once the prosthesis is properly fitted to the patient, the prosthesis is
shaped and smoothed and a solution of liquid plaster of Paris is sized
over irregular areas of the limb. However, care must be taken so as to
avoid the area 3 inches proximal to the ankle joint and any other areas
where the cured plaster could not be readily removed as described below.
Once the prosthesis is properly shaped, the inside of the socket is coated
with Vaseline.RTM. and filled with plaster and a vacuum pipe is inserted
therein in a conventional manner and let stand to cure. The foot section
14 is then removed from the keel 12 and the bottom of the keel 12 is then
machined in order to reach the configuration set forth in FIGS. 3 and 4 in
accordance with a preferred embodiment of the invention.
With a small hand-held grinder, a groove approximately 1/4 " wide and 150"
deep is machined about the entire peripheral edge of the bottom of the
keel as illustrated in FIGS. 3 and 4. Subsequently, approximately 1"
posterior of the leading edge of the keel 12, a transverse groove
extending from the lateral side 22 of the keel 12 to the medial side 24 of
the keel 12 approximately 1/2" in width and approximately 1/8" deep is
machined across the bottom of the keel 12. Again, the significance of such
grooves will become apparent from the below description. Next, a pair of
5/16" diameter bores are drilled in both the lateral 22 and medial 24
sides of the keel 12 to a depth of approximately 1/4". The first holes 26a
and 26c on either side of the keel 12 are drilled approximately 12"
anteriorly of the posterior of the keel 12 and the second holes 26b and
26d on either side of the keel 12 are positioned approximately 2"
anterior of the respective first hole.
Once the desired configuration of the bottom portion of the keel is
achieved, the vacuum pipe is again inserted into a pipe jig in order to
maintain the prosthesis structure in a horizontal fashion with the
anterior of the prosthesis facing upwardly. A knee-high stocking or other
similar covering material is pulled over the prosthesis and tied off at
the upper portion thereof. Any excess stocking accumulated at the bottom
of the keel can be forced into the bolt hole 13. A sheet of 1/8" copolymer
material, preferably polytetrabutylene, is heated to a temperature which
renders such material pliable, is then positioned adjacent the prosthesis
structure and subsequently vacuumed-formed thereover in a conventional
manner. A seam is formed on the bottom of the keel and along the posterior
section of the prosthesis. This seam is then trimmed to within 1/4" and
subsequently gently rolled with a dowel to form a smooth and inconspicuous
seam. This material is then allowed to cool for approximately 12 hours
before the excess plastic is removed. Once the material has cooled, all
plastic which overlies the raised portions 28 and 30 of the keel is
removed while the material within the grooves 18 and 20 remains. Further,
plastic material will subside into the bores 26a-26d. It can be noted that
upon the conclusion of the manufacturing process, the plastic material
which has been maintained within the grooves 18 and 20 will securely
retain the keel 12 portion within the now copolymer coated prosthesis.
The prosthesis is now in its final stages wherein the plaster is removed
from within the socket and a 1" spade drill bit is used to drill up into
the prosthesis from the bolt hole 13 in order to remove as much of the
foam material from within the copolymer shell as possible. The drilling is
continued upward through the distal end of the socket with care being
taken so as to not contact the copolymer coating. All of the foam material
is then removed from a point approximately 2" above the ankle joint seam
17 to the distal end of the socket. The already formed hole 16 in the
socket may be enlarged in order to facilitate removal of the foam
material. A router with a 40 grit cone can be used for quick and easy
removal of the foam material. Again, care must be taken in order not to
excessively contact the interior of the copolymer shell of the prosthesis.
It should also be noted that all foam material which can be removed without
jeopardizing the structural integrity of the prosthesis must be removed in
order to achieve as light a prosthesis as possible.
The exposed surfaces of the raised portions 28 and 30 are then sanded in
order to form a highly advantageous surface for adhering the foot 14 to
the bottom of the prosthesis. A plug having a diameter of approximately 1"
and a depth of approximately 5/16" and formed of PELITE.RTM. foam material
is snugly forced into the keel hole in order to seal off this opening. In
a similar manner, a plug is placed in the bolt hole of the foot in order
to provide a smooth and congruent bottom surface thereof.
The foot 14 is then positioned on the keel section and temporarily secured
in place by masking tape or other suitable material. A channel is thus
formed between the foot 14 and the keel 12 which readily receives adhesive
material therein. The masking tape is wrapped sufficiently around the foot
14 in order to provide only one small access opening to the channels in
the heel region of the foot 14 which are formed by the grooves 18 and 20,
the foot 14 and the masking tape. This will allow the adhesive material to
flow throughout the bonding surfaces between the foot 14 and the keel 12.
In accordance with the preferred embodiment, a mix of R200 epoxy resin and
hardener are used for this purpose. With the prosthesis positioned such
that the toe is pointed in a downward direction, the adhesive is poured
into the access hole left adjacent the heel of the foot 14. The adhesive
material will settle throughout the channels, therefore, the adhesive must
be periodically refilled. Once this is completed the prosthesis in its
present stage must be allowed to dry for at least 24 hours. Once
completed, any excess resin is removed and all of the surfaces of the
prosthesis are smoothed by using a fine grit sandpaper resulting in a
smooth and congruent prosthesis. The foot portion 14 may then be painted
any suitable color for cosmetic purposes. Further, cosmetic stockings can
then be put on the prosthesis for cosmetic improvement.
By manufacturing the prosthesis in accordance with the above-described
process, the overall weight of the prosthesis can be reduced from 31/2
lbs. to 11/2-2 lbs. without sacrificing any structural integrity.
Moreover, the user can be confident that the catastrophic failures
associated with previous prosthetic devices will not occur regardless of
whether the user is active or inactive.
While the invention has been described with reference to a preferred
embodiment, it should be appreciated by those skilled in the art that the
invention may be practiced otherwise and as specifically described herein
without departing from the spirit and scope of the invention. It is,
therefore, to be understood that the spirit and scope of the invention be
limited only by the appended claims.
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